cannot figure out what is causing my kt100 to run for about 3-5 seconds then shut off. Changed fuel, carb, filter, tci, plug. Still unchanged. Has spark out of cylinder, then put plug in and it runs for a few seconds then shuts off . Pull plug, no spark. Try agian same results. When it does run, revs fine sounds good then shuts off agian. Any thought where to start looking next?